Hi Soman,

These models will not work with and current CUCM Version :(

Q. What is the Cisco® Unified IP Phone 500 Series?

A. The Cisco Unified IP Phone 500 Series is a group of cost-effective, entry-level phones designed to work ***solely with the Cisco Unified Communications 500 Series for Small Business.

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/vcallcon/ps7293/qanda_c67-466070_ps9730_Products_Q_and_A_Item.html

Hardware Features and Enhancements

The Cisco 500 Series phones offer customers the option of having a 10/100 switch port for connecting to a co-located PC via a LAN connection, if needed. The Cisco Unified IP Phones 521SG and 524SG offer the 10/100 switch port, while the 521G and 524G models do not. Orderable now.

***These phones are designed for use with the Cisco Unified Communications 500 Series for Small Business only. They will not work with any other Cisco platform.

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps9730/prod_bulletin_c25-495153.html

Hope this helps!

Rob